This invention relates generally to lock nuts of the kind having a deformable elliptically-shaped threaded bore and, more particularly, to lock nuts of this kind that are specially configured to provide a high degree of flexibility with maximum reusability.
As shown in FIGS. 1 and 2 of the drawings, prior lock nuts of this general kind typically include a rigid body section and an integral deformable section projecting from one end of the rigid body section. A threaded bore extends axially through the two sections. The deformable section typically has a uniform radial thickness, with an arcuate periphery, although some lock nuts of this kind have included deformable sections with hexagonal peripheries that are mere extensions of hexagonal rigid body sections.
In manufacturing the prior lock nuts of this kind, two opposed sides of the deformable section are deformed radially inwardly into the threaded bore, such that that portion of the bore has a generally elliptical cross section. The ellipse's major and minor axes are oriented substantially perpendicular to each other. When the lock nut is threaded onto a bolt, the deformable section is deformed back into a generally circular cross section, to frictionally lock the nut in place.
When the lock nut is subsequently unthreaded from the bolt, the deformable section often fails to return fully to its original elliptical shape. This is because of over stressing or plastic deformation, particularly in the area of the ellipse's major axis. In the past, the usual practice has been to over-deform the ellipse and allow the initial threading of the nut onto a bolt to properly size the ellipse. Thereafter, it is hoped that with each repeated use the deformable section will deform only elastically, and not plastically. However, that hope frequently is not realized, and after only a few cycles of usage, the locking torque frequently reduces to an unacceptable level. When that occurs, the lock nut must be discarded and replaced with a new one. In addition, when the lock nut is threaded onto a bolt fabricated to the upper tolerance limits of its thread pitch diameter and thereafter removed and threaded onto a similar bolt fabricated to the lower tolerance limits of its thread pitch diameter, the resulting locking torque is frequently too low.
It should therefore be appreciated that there is a need for a lock nut of the kind having an elliptically-shaped threaded bore that can be repeatedly threaded and unthreaded on a bolt for a greater number of cycles than previously could be achieved, without experiencing an excessive reduction in frictional locking torque. The present invention fulfills this need.